Manufacture of polyesters



MANUFACTURE QEIIOLYESTERS 1 2,932,625 Patented Apr. 12, 1960 "iceinterchange reaction we have found that the colour of the highlypolymeric polymethylene terephthalate obtained is not good enough foruse as fibre or film-forming materials and that it has a low softeningpoint, as

William Robert Burton and Norman Standring, Blackley, 5 a result ofdegradation. To ensure that a good quality England, assignors toImperial Chemical Industries 1 polyester is obtained We prefer that thetemperature d, London, England, a corporation of Great h ld ot exceed280 C. t V Bntam In a particular form of our invention, ethylene glycolNo Drawin A licafion Febm 9 1956 1s reacted with dimethyl terephthalateto form polyg SeriglpNo. 1 3 4 ary 10 ethylene terephthalate. This isthe best known highly polymeric polymethylene terephthalate and hasgreat Claims priority, application Great Britain June 29, 1955 merit asa fil and fib f i materiaL 3 Claims (CL To increase the speed ofreaction, catalysts may be used for the ester-mterchange reaction andthe polyconhi invention r to h nufa ture f polyesters l5 densation. Forthe former lead oxide, zinc acetate or particularlylthe fibre-formingpolyesters known as the catcmm acetete are sfintablet whlle latter leadhighly polymericpolymethylene terephthalates. oxide and antimony madeare known to give good results. It thas been proposed in British patentspecification T fPnowmg example h h Parts are by No. 578,079 to makehighly polymeric polymethylene W lllustratee but does not t the scope ofour terephthalates'by a process comprising reacting a glycol mventlohofthe series .HO (CH ),,OH with terephthalic acid or a EXAMPLE 10waliphatic ester of terephthalif: acid and t n the The experimentalresults are listed in the table. The e on product to obtain esters m ahlghly p y specified quantities of ethylene glycol and dimethyl t h- 111the p l 0f the Process f thls P terephthalate are heated in a reactionvessel fitted with a fieatlfm It has been found that t e of Tahoe ofglyeel reflux condenser using as catalyst 0.015% of zinc acetate to 91esters 0f j p h field of less than 211 and 0.02% of antimony oxide.Ester-interchange takes YVhlle glvlllg Short teaetlen tlmes 011 the Veryh Scale place at atmospheric pressure and is complete when 512 in thelaboratory is not suitable for commerc1al operagm of methanol has beencollecwi The reaction mass U011, bee'flllse t larger batches of materielare used is then transferred to an autoclave fitted with a constant thereaction time moreases to such an extent as to be Speed agitator, Thetemperature i brought to 275 C ne 9 It has become statldal'fl Praetlcet0 and the pressure reduced to less than 1 mm. of mercury. use a glycolt0 Y ester of e t Polycondensation proceeds with elimination of glycolthan 2:1 to obtain economic reaction times. In British u til therequired molecular weight is attained The Patent speelfieetlen 578,979311 the examples e course of the polycondensation is followed bymeasuring Place at temperatures of 200 the increase in power inputrequired by the constant 18 because the Presence of the ltlltlel largequantifies speed agitator. In all cases the reaction is stopped when ofglycol in the reaction mixture ensures that some free a limit isattained known to correspond with an intrinsic glycol is presentthroughout the reaction, and prevents viscosityof 0.6-0.7.

' Table Ester Interchange Polycondensation Weight Weight EthyleneDnnethyl Molar lycol, Tereph Ratio Time Temper- Time Time Total TimeIntrinsic Sof Parts thalate, ature Temp., at in Vistening" Parts Range,0. 1mm. autccosity Point,

Hrs. Mins. O. clave Hrs. Mins. O.

1,552 25:1 4 35 147-208 275 1.15 2 7 25 .51 250.5 1, 552 1.311. a 54151-275 275 1.22 1 27 5 21 .54 259. 5- 1,552 2.51 5 07 1582l0 275 1.40 255 s 02 .55 250.2 1,552 1.411 t 20 150-254 275 1.15 1 20 5 40 .52 252.21,552 1.351 s 30 150-277 275 1.15 1 27 4 57 .55 268.1 1,552 1.55:1 a 55150-277 275 1.45 1 54 5 49 .51 258.5 1,552 1.31 4 00 150-291 275 2.25 231 5 51 .55 255.0 1,552 1.55:1 4 00 151-282 275 1.01 1 15 5 15 .52 255.0

temperatures of 200 C. being exceeded. Furthermore, it has beengenerally accepted that in a reaction mixture containing any freeglycol, heating above 200 C. is undesirable because of the tendency fordiscolouration of the product.

According to the present invention we provide a process for makinghighly polymeric polymethylene terephthalates, wherein a glycol of theseries HO(=CH ),,OH, where n is an integer from 2 to 10, is reacted inan ester-interchange reaction with a di-alkyl ester of terephthalic acidand the product heated until polycondensation takes place and a highlypolymeric polymethylene terephthalate is obtained, characterised in thatduring the ester-interchange reaction the temperature exceeds 210 C. butdoes not exceed 300 C. and that the glycol to dialkyl terephthalatemolecular ratio is less than 2:]. Preferably the ratio is in the range1.5 :1 to 1.3:1.

1 If temperatures of 300 C. are exceeded in the ester- From the resultsin the table it can be seen that using: molar ratios of less than 2:1glycol to dimethyl terephthalate, the total reaction time is lower thanwhen high ratios are used and the product obtained is in no wayinferior, as shown by intrinsic viscosity and softening. pointmeasurements. Using these low glycol ratios greatly reduces the amountof glycol distilling ofi during the polycondensation step, which, in anycommercial. process, must all be reclaimed and purified for use again.Furthermore, the reduction in glycol content of the re-- action massenables a greater amount of dimethyl tereph thalate to be present in thereactor and thus increases the production rate.

In the example, it will be seen that the reaction takes place in tworeaction vessels. Previously, when temper-- atures for theester-interchange have not exceeded 200 C. it has been necessary, ontransferring the products of ester-interchange to the polyoondensationautoclave, to-

raise the temperature of themass to 275 0., thus wastchange topolycondensation takes place it is necessary to reduce the pressure' to1 mm. of mercury. Using an initialglycol/dimethyl terephthalate ratiogreater than 2:1 in commercial production, as in the prior art, thisreduction in pressure must be a slow process as any efiort to reducepressure quickly with glycol present, causes excessive frothing of thereaction mass and tends to cause blockages in the vacuum lines to thereaction vessel. This in turn tends to prolong the polycondensationtime. When the lower glycol/dimethyl terephthalate ratios of'ourinvention are used there is far less glycol present at the end of theester-interchange reaction. This reduces the tendency to frothing andenables the pressure to be reduced more quickly with no fear ofblockages occurring and leads to a considerable saving in time. Thesaving in polycondensation time obtained using the process of ourinvention can be clearly seen from columns 7 and 8 of the table. Usingthe lower glycol ratios the difference between the time the reactionmass is held at a pressure of 1 mm. and the total time in the autoclaveis very small. With the higher ratios this difference is much greater.

The saving in total production time is shown in "column 9. 1

What we claim is:

1. A process for making highly polymeric polymethylene terephthalates bypolycondensation of the esterinterchange reaction product which has beenprepared by, reacting ethylene glycol under atmospheric pressure with adi-lower alkyl ester of terephthalid'acidat an ester-interchangetemperature rising in excess of about 210 C. but less than about300f..C. .with the molarratio of said glycol to said di-lower alkylterephthalate ester between 13:1 and 2:1, thereafter reducing thepressure to less than about 1 mm. of mercury without reducing thetemperature, and conducting said polycondensation step at a temperatureof about 275 C. until an intrinsic viscosity of from about 0.6 to-0.7 isattained;

2. A process according to claim 1, wherein said ratio is in the range1.5:1 to 1.3:1. a 3. A process according to claim -1, wherein saidester- 20 interchange temperature does not exceed 280 ;C.'

References Cited in the file of this patent UNITED STATES PATENTS],Whinfield et'al. Mar.' 22, 1 949 Auspos et al. June 30, 1953 OTHERREFERENCES Hardy: J.S.C.I., 67, 426-32, November 1948.

1. A PROCESS FOR MAKING HIGHLY POLYMER POLYMETHYLENE TEREPHTHALATES BYPOLYCONDENSATION OF THE ESTERINTERCHARGE REACTION PRODUCT WHICH HAS BEENPREPARED BY REACTING ETHYLENE GLYCOL UNDER ATMOSPHERE PRESSURE WITH ADI-LOWER ALKYL ESTER OF TEREPHTHALIC ACID AT AN ESTER-INTERCHANGETEMPERATURE RISING IN EXCESS OF ABOUT 210*C. BUT LESS THAN ABOUT 300*C.WITH THE MOLAR RATIO OF SAID GLYCOL TO SAID DI-LOWER ALKYL TEREPHTHALATEESTER BETWEEN 1.3:1 AND 2:1, THEREAFTER REDUCING THE PRESSURE TO LESSTHAN ABOUT 1 MM. OF MERCURY WITHOUT REDUCING THE TEMPERATURE, ANDCONDUCTING SAID POLYCONDENSATION STEP AT A TEMPERATURE OF ABOUT 275*C.UNTIL AN IN INTRINSIC VISCOSITY OF FROM ABOUT 0.6 TO 0.7 IS ATTAINED.